sedimentary
Fossiliferous Limestone (Crinoidal Limestone)
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 3 (Mohs scale); Color: Brown to tan matrix with white fossil inclusions; Luster: Dull/Earthy; Crystal structure: Macro-fossiliferous; Reaction: Effervesces with dilute hydrochloric acid.
- Hardness
- 3 (Mohs scale)
- Color
- Brown to tan matrix with white fossil inclusions
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Brown to tan matrix with white fossil inclusions; Luster: Dull/Earthy; Crystal structure: Macro-fossiliferous; Reaction: Effervesces with dilute hydrochloric acid.
Formation & geological history
Formed in shallow, calm marine environments whereby the remains of marine organisms, specifically crinoids (sea lilies) and brachiopods, settled on the seafloor and were lithified over millions of years. This specimen likely dates from the Paleozoic era.
Uses & applications
Used primarily for fossil collecting, educational purposes, and as a decorative stone. Large deposits are used in the production of cement and crushed stone for construction.
Geological facts
The white circular and 'donut' shapes visible are cross-sections of crinoid stems, which were animals related to starfish, not plants. They were so abundant in ancient seas that they often formed entire rock layers.
Field identification & locations
Identify in the field by looking for distinct white circular or screw-like patterns (fossil stems) embedded in a finer-grained matrix. It is commonly found in areas of the Midwest US, UK, and other regions with exposed ancient seabed strata.
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